text: 
  var image = ee.Image('LC8_L1T/LC82040242013139LGN01');
  
  var wbi = image.expression(
      'blue/nir',
      {
          blue: image.select('B2'),    // BLUE
          nir: image.select('B5'),    // NIR
      });
  
  
  Map.centerObject(wbi);
  Map.addLayer(wbi);
  
  